New Data on Activity Coefficients of Potassium, Nitrate, and Chloride Ions in Aqueous Solutions of KNO3 and KCl by Ion Selective Electrodes

Ion selective electrodes (ISEs) are used to measure the single-ion activity coefficients in aqueous solutions of KNO3 and KCl at 298.15？K against a double-junction reference electrode. The EMF responses of ISEs up to 0.01？m are plotted to obtain the slope and intercept values. The obtained slopes and intercepts are used in Nernst equation for higher concentrated solutions for calculation of individual ion activity coefficient. The mean ionic activity coefficients are estimated from single ion activity coefficient, and the obtained results are compared with the literature values. 1. Introduction Activity of a species in a solution is referred to as its effective concentration in that solution. In very dilute solution as interactions are insignificant, concentration and effective concentration are the same. But as the concentration increases, the electrostatic interaction increases and deviations from ideality are accommodated by modifying the concentration with activity coefficient. When the solute undergoes ionic dissociation in solution, then we can define activities of cations and anions , so also activity coefficients . The knowledge of individual ionic activity coefficients is important for the design of equilibrium processes involving electrolyte solutions as well as for processes involving ion exchange and pollution control [1]. Activity coefficients can also be used for the prediction of rate constant, equilibrium constant, chemical potential value, and solubility product and for the separation of a species from a mixture of substances on the basis of their high or low activity coefficient. Single-ion activity coefficients are traditionally termed as not measurable by simple thermodynamic methods due to space charge interactions. But people have tried to measure single-ion activity coefficient of nonvolatile electrolytes in solution by two methods: (1) solvent activity method involving vapour pressure and Gibbs-Duhem equation and (2) electrochemical cell technique involving direct calculation of the activity of an electrolyte by measurement of EMF of ions in an electrochemical cell. In recent past, Vera and coworkers [2–5] and few other researchers [6–9] demonstrated the application of ion selective electrode (ISE) technique for measurement of single-ion activity coefficients. The same approach has been utilized to find out the single-ion activity coefficient in this work. The coefficients are used to find out mean ionic activity coefficient for different salts. Most of the groups working on electrolyte solutions have given information on